In the sport or amusement of rolling hoops along the ground, particularly by children, many trundles have been devised to aid in the control of same, exemplary of which are those disclosed in my U.S. Pat. No. 3,827,180, prior art cited therein, and many others. While the various trundles have reached a high degree of perfection in the control of movement of a hoop, which is desirable for beginners in the sport, this desirability can be disadvantageous to those who have mastered their use in that what was originally a challenge to one's skill becomes monotonous and thus causes loss of interest and premature abandonment of the sport. Part of this is probably due to the design of the prior art hoops which have been constructed in substantially true circular form which rotate about the geometric center of a circle and which thus have a predictable stability, rotational velocity and direction of movement. As an example of the foregoing, the trundle operator may walk or run behind the hoop at constant velocity and the hoop rolls along the ground at constant forward velocity while rotating about its center at constant angular velocity, the only controls necessary being to change its direction of movement when desired or necessary or to accelerate or arrest its motion, which latter involves only a change of speed of the operator. Thus, while the operator may move at desired constant speed, may accelerate or decelerate to a new speed, these changes result only due to his desire rather than being compelled to do so by reason of the hoop design. As will be apparent, if the hoop design compelled the operator to make periodic changes in his velocity, a new skill, not heretofore required with a circular hoop, would be required.
Another disadvantage of the prior art resides in the nonadjustability of the diameter of circular hoops. The skill required to propel a hoop varies with its diameter, hence, an operator must procure a number of hoops of various fixed diameters if he desires to test his skill with hoops of different sizes.